Generally, the amount of use of services fluctuates with such factors as timing. As a result, a storage system has to keep ready for its storage region having a performance level that can meet the demand in a situation in which the amount of use most increases in a large enough capacity for storing the increasing information. However, as investments in information system do not increase rapidly, inability to make available a required storage region is posing a problem.
In this connection, according to Patent Literature 1, where a storage system is provided with a storage region having a plurality of different characteristics (including input/output performance and bit cost), written-in data is split into fragments of a fixed size known as pages, and the pages are arranged in a storage region manifesting designated characteristics. And there is disclosed a technique by which the storage system, after data is arranged in the storage region manifesting the designated characteristics, rearranges in the storage region having an appropriate input/output performance according to the frequency of accessing the pertinent pages by a host computer.
For the convenience of description, hereinafter the storage region manifesting a plurality of different characteristics and provided in the storage system will be referred to as a storage tier, and each of the storage regions constituting the storage tier, as a tier. Further, processing to arrange pages in the storage tier and processing to rearrange pages will be referred to as hierarchical control.
According to Patent Literature 1, in generally expensive storage regions (to be referred to as superior tiers) with high input/output performance, it is possible to arrange only such data as requiring that performance, but when the use of the service abruptly increases, the data to be accessed by the service may not be arranged in any superior hierarchical storage. As a result, possibility for the information system to complete the service within the expected length of time poses a problem.
In view of this circumstance, Patent Literature 2 discloses a technique by which, where a response performance required to be satisfied by data used in an application program (hereinafter, an application program may be referred to simply as an application) (to be referred to as a response performance requirement) is assigned, the pertinent file is arranged in a memory device having an appropriate input/output performance for satisfying the response performance requirement is disclosed. According to Patent Literature 2, a delay or a stop in the processing of the application can be prevented by permanently arranging the data to be used by the application in a storage region satisfying the response performance requirement.